RT5800
during the LSFET on-time. Once the current rises
above the LSFET valley current limit (I
LIM_L
), the
on-time one-shot will be inhibited until the inductor
current ramps down to the current limit level (I
LIM_L
),
that is, another on-time can only be triggered when the
inductor current goes below the LSFET current limit. If
the output load current exceeds the available inductor
current (clamped by the LSFET current limit), the
output capacitor needs to supply the extra current so
that the output voltage will begin to drop. If it drops
below the output under-voltage protection trip threshold,
the IC will stop switching to avoid excessive heat.
Output Under-Voltage Protection
The RT5800 includes output under-voltage protection
(UVP) against over-load or short-circuited condition by
constantly monitoring the output voltage V
OUT
. If V
OUT
drops below the under-voltage protection trip threshold
(typically 50% of the internal reference voltage), both
HSFET and LSFET will stop switching. Register
0x37[3], 0x38[3] and 0x39[3] can select hiccup or latch
protection behavior of each Buck converter when
converter is in UV condition. For hiccup behavior, both
HSFET and LSFET keep low state in a 1ms and then
IC starts to switch. If the output voltage is not greater
than UV threshold after internal soft-start end signal is
triggered, both HSFET and LSFET will still keep low
state again for next cycle. When each Buck is set to
latch mode, UVP will let converter enter shutdown
mode unless resetting IC by external EN pin or falling
to UVLO low threshold.
Over-Temperature Protection
The RT5800 includes an over-temperature protection
(OTP) circuitry to prevent overheating due to excessive
power dissipation. The OTP shuts down switching
operation when junction temperature exceeds a
thermal shutdown threshold T
SD
. Once the junction
temperature cools down by a thermal shutdown
hysteresis (T
SD
), the IC resumes normal operation
with a complete soft-start. It can select not to shut down
IC when OTP happens by using register 0x30[3].
Note that the over temperature protection is intended to
protect the device during momentary overload
conditions. The protection is activated outside of the
absolute maximum range of operation as a secondary
fail-safe and therefore should not be relied upon
operationally. Continuous operation above the
specified absolute maximum operating junction
temperature may impair device reliability or
permanently damage the device.
Copyright © 2019 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS5800-00
November 2019
www.richtek.com
9
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
